Method and apparatus for twisting and plying strands



A. W VIBBER Oct. 27, 1964 METHOD AND APPARATUS FOR TWISTING AND FLYING STRANDS 2 Sheets-Sheet 1 Filed April 24, 1963 INVENTOR. 111). J/QMW A. W. VIBBER Oct. 27, 1964 METHOD AND APPARATUS FOR TWISTING AND FLYING STRANDS Filed April 24, 1963 2 Sheets-Sheet 2 United States Patent M 3,153,893 METHQD AND APEARATUS FfiR 'IWISTING AND FLYING STRANDS Alfred W. Vibber, W. Englewocd, Teaneck, NJ. (560 Riverside Drive, New Yuri; 27, N31.) Filed Apr. 24, 1963, Ser. No. 275,416 12 Claims. (Cl. 57-583) This invention relates to a method and an apparatus for twisting and/ or plying strands, and particularly relates to a method of and an apparatus for plying strands together by rotating one strand about a source of supply of another strand, and plying the strands together beyond such source of the other strand.

This application is a continuation-in-part of application Ser. No. 261,704, filed December 14, 1951, and of application Ser. No. 4,973, filed January 27, 1960. Application Serial No. 261,794 is a continuation-impart of application Serial No. 223,189, filed April 27, 1951 (now abandoned).

Reinforcing cord such as that employed in automobile tires, V-belts, and the like usually consists of two strands twisted about each other but themserves having a relatively low twist. Such cord has been made in the past by twisting the two singes st ands separately in the same direction, following which the twisted singles strands are doubled by being twisted togedaer in the direction opposite the direction of twist of the singles strands. Such method involves three separate twisting operations, and, when the twisted singles strands do not d w continuously to the doubling spindle, also involves the taking up and the paying out of twisted singles strands.

To reduce the umber of operations involved in the making of such cord, as well as the number of twisting spindles required with their space and power require ments, a number or" different single spindle devices of the skip type have been proposed. in one of these types, such as shown in Clarkson Patents Nos. 2,503,242 and 2,729,051 the two singles strands are fed at substantially constant speed by separate constantly driven capstans to a plying point from which they are withdrawn under substantially constant tension. In another type of plying spindle the strand to be ballooned enters the ballon through a storage disc, the outer ballooning strand, being plied with an inner strand at a floating plying point near the apex of the balloon. In yet another type, such as shown in my prior Patent No. 2,857,730 and Clarkson Patent No. 2,986,865, the singles strands are fed toward the plying point by separate capstans driven at constant speed, and are vithdrawn from the plying point at a variable speed, such speed being governed by variations in the tension of the outer, ballooning strand.

The apparatus and method of the present invention eliminate the need for a constant tension takeup of the plied strands, with its attendant complications and need for frequent maintenance. At the same time, it gives much closer control of the plied cord from the standpoint of uniformity than does plying apparatus employing a floating plying point. Further, the apparatus and method of the invention take up the plied cord at constant speed, thereby producing cord of a high uniformity of twist.

The present invention has among its objects the provision of a novel simplified plying spindle of the skip type.

Another object of the invention lies in the provision of a novel spindle of the indicated type wherein the taking-up of the plied strand from the plying point takes place at substantially constant speed, whereby the desired number of twists per unit length of the plied cord may be accurately maintained throughout the length or" the cord.

A further object of the invention lies in the provision of a spindle of the skip type wherein correlation between 3,153,893 Patented Get. 27, 1964 the tensions in the two strands approaching the plying point is more easily achieved, and wherein such tensions may both be readily adjusted.

Another object of the invention lies in the provision of a novel method of plying a plurality of strands by a skip twisting operation.

The above and further objects and novel features of the invention will more fully appear from the following description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only, and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

FIG. 1 is a fragmentary view in side elevation of a first embodiment of a spindle for plying strands together to form a cord in accordance with the present invention;

FIG. 2 is a view in side elevation on an enlarged scale of the balloon size controlling mechanism employed in the apparatus of FIGS. 1 and 3;

FIG. 3 is a fragmentary view in side elevation of a second embodiment of twisting and plying spindle in accordance with the present invention; and

FIG. 4 is a fragmentary somewhat schematic view in tilted plan of the combined capstan employed in the apparatus of FIG. 3 which serves to feed the outer singles strand toward the balloon at constant speed and the plied cord away from the plying point at constant speed.

As will be apparent from the above, two embodiments of apparatus in accordance with the invention are shown herein, the first embodiment being shown in FIG. 1 and the second being shown in FIGS. 3 and 4. Both embodiments employ the balloon control device more specifically shown in FIG. 2. As will be more readily apparent below, the two embodiments of apparatus differ, not only as to the specific means employed to feed the outer, ballooned strand into the balloon and to withdraw the plied cord from the plying point, but as to the manner of variation of the tension existing in the ballooning strand upon changes in the diameter of the balloon, and as to the role played by the plying point in conjunction with the balloon control device in restoring the balloon to such diameter as to cause the strand in the balloon to be under a desired predetermined tension.

Turning now to FIG. 1, the plying spindle there shown is generally designated by the reference character 10. Spindle it) has a vertically disposed centrally hollow main shaft 11 which is rotatably mounted in a suitable bearing in a housing 16 ad'iixed to a supporting frame 12. The shaft 11 is driven by a belt 14 entrained over a pulley 15 affixed to shaft ill, the belt being driven by a suitable power source such as an electric motor, not shown. Supported on shaft 11 by a bearing contained in a housing 19 is a support 17 which is held from rotation by pairs of coacting lower and upper magnets 29 and 21 mounted on housings 16 and N, respectively.

A package support 22 is mounted on support 17, support 22 having means for holding a strand package 24 centrally thereon. Package 24, which supplies the inner strand b, is surrounded by a cage-like guard 23, a part of which also functions to tension the strand b preliminarily in the travel of such strand downwardly to a guide pulley 25 mounted on support 17. The spindle 10 as thus far described is generally similar to that shown and described in Clarkson Patent No. 2,689,449.

The strand handling device 26 on support 17 of the present apparatus is an idle strand tensioning means which is preferably adjustable to vary its strand tensioning effect. The tension device 26 shown is generally similar to that shown in FIG. 5 of the patent to Klein No. 2,671,305, changed as to its orientation and the manner of feeding the strand into and away from the tension device. It is to be understood that other known strand tensioning devices may, if desired, be substituted for the tensioning evice 26 here shown and described.

The strand b, after passing under guide pulley 25,

travels to the right (FIG. 1) initially to contact the right hand roller 27 at the bottom thereof, and then travels counterclockwise around the roller to contact the left hand roller 29 adjacent the bottom thereof. travels clockwise around roller 29 and between such roller and an adjustably tensioned leaf spring 3%) which has a curved free end overlying and conforming to the curvature of the roller 29. As set forth in the above Klein patent, the ends of the shafts mounting rollers 27 and 29 are supported in guideways (not here shown) which lie generally parallel to the direction of the runs of the strand approaching roller 27 and leaving roller 29, the tension in the strand and the force exerted on the roller 29 through strand 1: by the leaf spring 39 causing the strand to be nipped forcibly between the rollers. The leaf spring 39 is secured at its upper end to support 17; the spring is adjustably thrust toward roller 29 by a set screw threaded into a bracket affixed to support 17.

From the top of roller 29 the strand [2 travels to the right to a roll guide set 31, and thence progresses to a canted fixedly journalled guide roll 32 which directs it downwardly centrally into the open upper end of the hollow main shaft 11 of the spindle. Strand [1 is pulled downwardly through the bore in shaft 11 to meet and be plied with a second strand a at a plying point X within the shaft.

The strand a is supplied by an outer strand package 34 mounted on a fixed package support having a central package guide 35. From package 34, after being preliminarly tensioned by means not shown, the strand a proceeds to a capstan set 36 which feeds it forward at substantially constant speed. Capstan set 36 may be constructed and driven in the same manner as the capstan for feeding the strand there designated b in FIG. 8 of Clarkson Patent No. 2,729,051. Capstan set 36 of the present apparatus has two vertically spaced rollers 37, 39, both driven in synchronism with shaft 11, the lower roller 39 being tipped at a small angle, as shown. Strand a travels about rollers 37, 39 a plurality of times in laterally spaced wraps, passing between roll 37 and a spring pressed idle roll 40, and then leaves the capstan set at the bottom of roller 39 to travel about a fixedly mounted guide pulley 41. From pulley 41 the strand proceeds upwardly to a further fixedly mounted guide pulley 42 which is mounted on a cross arm 44 secured to a fixed standard 45 rising from frame 12. From pulley 42 the strand travels to a further pulley 46, journalled on a bracket 47 affixed to cross arm 44, from which it proceeds downwardly to an apex guide for the balloon 51 formed in strand a by the spindle.

The apex guide is here shown as being a part of a balloon control device 49 which is similar to that disclosed in Clarkson Patent No. 2,689,449. Such device 49 includes means for sensing changes in the diameter of the balloon, and means responsive to the first named means for changing the size of the balloon. The balloon control device disclosed and claimed in applicants pending application Ser. No. 261,704, filed December 14, 1951, may, if desired, be substituted for device 49 herein. It is to be understood that other balloon control devices performing generally the same functions and achieving generally the same result may be substituted in the dis- The strand then closed combination for the balloon control device 49 ll thence generally radially and somewhat downwardly beneath the flyer disc into an opening in the side of shaft 11, in a manner similar to that shown in FIG. 6 of Clarkson Patent No. 2,729,051. Within the bore in shaft 11 generally below the radial passage through the sidewall thereof there is affixed a cord forming die (not shown) within which equal lengths of the strands a and b are wrapped about each other at the plying point X. After leaving the plying point, the now formed cord 0 travels downwardly through the bore in shaft 11, out the bottom end thereof, and downwardly to a fixedly mounted guide pulley 52.

From pulley 52 the cord 0 travels upwardly to a second capstan set 54 which is similar to the above described capstan set 36. The opposed vertically spaced rolls 55, 56 of such capstan set are driven at a constant speed from and synchronized with the shaft 11. The cord passes around rolls 55, 5-6 a plurality of times in laterally spaced wraps, being nipped between roll 55 and an idle roll 57 which is spring pressed toward roll 55. From the capstan set 54 the cord 0 travels downwardly at substantially constant speed to a take-up bobbin 59 which is frictionally rim-driven by one or both of its supporting rolls 60.

Turning now to FIG. 2, the construction of the balloon apex guiding and balloon control mechanism 49 is shown in detail. A nut 61 is mounted in a vertical opening adjacent the outer end of arm 44 and is retained therein by a set screw 58, as shown. An elongated, externally threaded, hollow spindle 62 is rotatably mounted in nut 61, the bore 63 in such spindle receiving the strand a as it passed downwardly from pulley 46 into the balloon 59. The lower end of the spindle 62 has a radially outwardly extending flange 64 integral therewith, and a vertically rounded annular portion 65 inwardly thereof at the bottom of bore 63, the most constricted zone of portion 65 forming an annular guide for the apex of balloon 50.

Coaxially afiixed to the spindle 62 so as to rotate therewith is a bell-shaped sheet metal element 66 having a radially inwardly projecting annular upper end 67 which overlies and engages flange 64 on the spindle. Element 66 is retained on the spindle by a nut 69 which is tightly screwed down upon the portion 67 of element 66. The element 66 has a somewhat outwardly flared smooth annular lower rim 7%), the element 66 being of such shape that during running of the spindle the rim 7i) and the strand a in balloon 50 contact each other in the manner shown in full lines in FIG. 2.

The ballooning strand a thus tends to turn the element 66 and the spindle 62 attached thereto in the direction of rotation of the balloon. The hand of the threads in nut 61 and on spindle 62 is such that rotation of such elements in the direction of rotation of the balloon causes a lowering of the spindle 62 with a consequent decrease in height of the balloon 50; The torque imposed upon spindle 62 through element 66 by the balloon is opposed by a coil torque spring 71 which is disposed about the spindle'62 below nut 61, the spring having a lower tang 72 aflixed to nut 69 and, in the embodiment shown, an upper tang 74 aflixed to arm 44 as by a set screw or stud 75. If desired, in an unillustrated modified embodiment, the torque imposed by spring 71 upon spindle 62 may be adjusted during operation of spindle by providing an annular member to which tang 74, suitably extended is secured, such annular member being rotatably mounted on arm 44 and adjustable about its axis in order thus to adjust the spring. I

The balloon control 49 functions in the manner de scribed in Clarkson Patent No. 2,689,449. Thus, when the diameter of balloon 50 becomes too large, the spindle 62 is turned to decrease the height to the balloon, for example, to that of the balloon shown in phantom lines in FIG. 2 and designated 59'. When the diameter of the balloon becomes too small, the control 49 functions to increase the height of the balloon. When balloon height increases, the tension of strand a in the balloon increases,

and when the balloon height decreases, the tension of the strand a in the balloon decreases.

In the above-described apparatus and method, the balloon 50 is the type having a single bulge. The maximum diameter of the balloon lies above the flyer 51, and usually somewhat below the mid-point of the distance between the flyer and the apex guide. With such balloon, with a constant weight per unit length of the ballooning strand, the tension in the ballooning strand decreases as the diameter of the balloon increases. The tension in the inner strand remains substantially constant. Under such conditions the plying point X tends to serve as a compensator to restore the balloon to a desired diameter should it deviate appreciably therefrom. Thus, when the balloon increases in diameter from such desired diameter the inner strand b tends to become the core at the plying point, a greater length of strand (1 than of strand b is absorbed into the plied cord in a given time, and the balloon diameter is thus decreased. The reverse action takes place when the balloon diameter becomes less than the desired diameter.

When the unit weight of the outer ballooning strand varies appreciably, however, particularly if such weight increases, the plying point X ceases to be effective as a compensator to restore the balloon to the predetermined desired diameter; in fact, the plying point then functions to make the system unstable. Thus, assuming a substantial increase in unit weight of the ballooning strand 0, the tension in the balloon Sit increases when balloon diameter increases due to the great increase in the efiect of centrifugal force upon the strand tension. Because the tension of the outer ballooning strand :1 now exceeds the tension in the inner strand 5, which remains substantially constant, the outer, ballooned strand tends to become the core of the plied strand at the plying point, thereby causing less of the outer strand to be absorbed into the plied cord, and causing the balloon to increase still more in diameter.

The automatic balloon control device 49 shown herein functions to supplement the action of the plying point X as a balloon compensator when the unit weight of the ballooning strand remains substantially constant. Not only that, but such balloon control device functions in coordination with the plying point to correct variations in balloon diameter caused or accompanied by variations in the unit weight of the ballooning strand. It accomplishes such latter result by decreasing the height of the balloon when the balloon, regardless of the cause, increases in diameter, from a predetermined desired value, and by increasing the height of the balloon when the balloon, regardless of the cause, decreases in diameter from such predetermined desired value. The tension of the strand a is thus decreased and increased, repectively, so that the plying point X may then function to cause more and less, respectively, of the ballooning strand :2 to be absorbed into the plied cord 0. As a result, the diameter of the balloon is restored to the predetermined desired value.

In the embodiment of the apparatus shown in FIGS. 3 and 4, the spindle is generally designated by the reference character 78. Such spindle is supported on a frame 79 having a horizontal enclosure portion 89 within which is contained driving mechanism for the hollow main vertical shaft 31 of the spindle which is rotatably mounted in a bearing housing 82 secured to enclosure portion 89. Non-rotatably mounted on shaft 81 is a fixed support 84 upon which a package support 85 is mounted in turn. An inner strand package 86 on support 85 supplies an inner strand b. Strand 1) is paid off package 36, travels upward and then across the top of the package as indicated in dash lines in FIG. 3, and then proceeds downwardly to pass through a pretensioner 87 of the spring pressed washer type. From pretensioner 87 the strand b passes to a tensioning device 89 which is similar to the device 26 of the first disclosed embodiment. Strand b passes counterclockwise about roller 90 of device 89, then clockwise around roller 91 thereof and between such roller and an adeases 6 justable leaf spring 92. From roller 91 the strand 1) travels successively about guides 94 and 95 to pass about a canted central guide roller 96 and thence centrally down into the bore of the hollow main shaft 81 of the spindle.

The outer, ballooned strand a is fed to spindle '78, in a direction from right to left, as from a multiple end beam as in Clarkson Patent No. 2,986,865. Strand a passes through a fixed guide 97 on the frame of the spindle, to a further fixed guide 9, and thence upwardly and to the right to a first, singles feeding portion of a combined capstan device generally designated 1%. The construction and manner of operation of capstan 106 are illustrated most clearly in FIG. 4. Projecting forwardly from housing Si is a horizontal shaft 161 which is driven in synchronism with and by the main shaft 81 of the spindle by means such as gears not shown. Secured to shaft 101 is a stepped roller having a larger, forward circular cylindrical portion 192. Mounted on a bearing on a fixed, undriven stub shaft 1&5 projecting forwardly from housing 39 at a point spaced from shaft 1ll1 is an idle roller 1%. The outer strand 0 rises from guide 99 to pass clockwise over driven roller 1&2, passes over idle roller 1%, and then repeatedly passes around such rollers in spaced runs, finally leaving roller 102 to .pass to the right under a fixed roller guide 199, up partially about a fixed roller guide 119, thence to a roller guide 111 on a cross arm 112 on standard 115, and finally to an apex guide and balloon control device 49 which has the same construction and function as the device. designated by the same reference character in FIGS. 1 and 2.

The described portion of the composite capstan is provided with an idle presser roller 1% mounted on a lever 107 which is spring pressed to nip the runs of strand a between it and roller 1 92. The strand a is thus forwarded at substantially constant speed to the device 49 and thence into the balloon which in this instance has an upper portion 113 and a lower portion 114.

The balloon is generated by a flyer disc 116 which is fixed to shaft 31 of the spindle to rotate therewith. The strand a passes through an eye 118 in the outer edge of disc 116, and thence generally radially inwardly to pass into an opening through the wall of shaft 81 to a cord forming die at the plying point X where equal lengths of strands a and b are wrapped about each other to form cord 0.

From the plying point X the cord 0 passes down through the lower end of the hollow main shaft 81 and thence downwardly to a fixedly mounted guide roller 117. From roller 117 cord 0 rises to pass over the inner, smaller diametered circular cylindrical portion 119 of the stepped roller affixed to driven shaft 1111. The cord 0 then passes over an inner idle guide roller 12%) rotatably mounted on shaft 105. Roller 120 is separate from and rotates independently of roller 104. After passing in multiple spaced runs about rollers 119 and 1213, the cord c leaves the capstan by passing downwardly partially around roller 120 to a fixed guide 124 and a movable guide 125 which is traversed by means not shown to lay the cord upon a bobbin 126 which is frictionally rim driven by a pair of rollers upon which it rests. One such driving roller, designated 127, is shown .in FIG. 3 driven by means generally designated 129.

The portion of the capstan 169 which forwards cord 0 from the plying point X does so at substantially constant speed. Slippage of the cord on roller 119 is minimized by an idle presser roller 121, which is separate from and independent of presser roller 106. Roller 121 is mounted on a lever 122 which is spring pressed to urge the roller 121 forcibly against the portions of the cord lying between rollers 11% and 121.

The spindle 78 is provided with an auxiliary idle flyer 130 having an arm 131 with a guiding eye 132 therein through which the strand a of the balloon passes. Flyer 139 has an arm 134 extending oppositely from arm 131 for the purpose of counterbalancing the flyer. The bearing 135 for the fiyer 130 is mounted on the removable lid 136 of an enclosure 137 disposed about package 86 and supported on the non-rotatable member 84 on shaft 81. 7

As shown, the eye 132 of the auxiliary flyer 130 lies outwardly of the shaft 81 of the spindle 78 at a radial distance which somewhat exceeds that of the eye 118 through the flyer disc 116. The upper portion 113 of the balloon thus always lies in the first quadrant, that is, the strand a always enters the eye 132 of the auxiliary flyer at an angle which is less than 90", measured inwardly toward the axis of the flyer, between the plane of rotation of the flyer and a normal thereto at eye 132. -It has been found that the use of the auxiliary flyer 130 permits the use of a higher tension of strand a in the balloon and a higher speed of rotation of the spindle shaft 81 than would be permissible without it, and that the auxiliary flyer assures the maintenance of portion 114 of the balloon free from contact with any fixed structure such as the lid 136 or the body 137 of the guard about package 86.

With the system of FIGS. 3 and 4, the tension conditions are somewhat different from those existing in the system of FIGS. 1 and 2. The auxiliary flyer 130 acts in effect to create and maintain a short balloon 113 between it and the apex guide of device 49, the tension in such short balloon apparently being the primary determining factor as to the tension existing in the entire revolving loop 113, 114 which consists of the short balloon 113 and the length of rotating strand in the balloon portion 114 between the auxiliary flyer and the driven flyer disc 116. Such length of strand in balloon portion 114 serves primarily to drive the auxiliary flyer; in any event, the tension variations caused by variations in the length of strand in portion 114 of the balloon are additive to those of the short balloon 113.

The short balloon 113 is a single balloon which spins above the bulge, that is, the balloon 113 has no true maximum diameter at all because such bulge is situated in the imaginary continuation of the short balloon 113 below the auxiliary flyer 130. In such short balloon 113 the yarn tension is high, and an increase in the di-' ameter of the short balloon 113 results in a greater yarn tension. See pages 20 and 21 of Balloon Control, by Grishin, revised and reprinted by T.M.M. (Research) Limited, from Platts Bulletin, copyright 1956 by Platt Bros. (Sales) Limited, Oldham, England.

In the system of FIGS. 3 and 4 the plying point X never is, by itself, a compensator for variations in balloon diameter. The use of the auxiliary flyer thus requires for all conditions of operation of the apparatus, that is, with yarn of uniform or yarn of varying unit weight, a balloon compensator which responds to variations in balloon diameter. This follows from the fact that with an increase in the diameter of the balloon the tension in the strand a increases, whether the weight per unit length of the strand remains constant or increases. Thus, the plying point per se cannot function to restore the balloon to the diameter at which the balloon has the desired tension equalling that imposed upon stand b as it approaches the plying point.

The plying point X, however, acting in conjunction with the balloon control device 49, maintains the balloon 113, 114 under stable control. Thus, upon an increase in diameter of the balloon, regardless of the cause, the device 49 acts to decrease the height of balloon portion 113, and 'thus to decrease the tension in strand a as it approaches the plying point. Upon such decrease of tension in strand a, the plying point functions to cause strand a to be absorbed into the cord at a greater rate, thereby decreasing the diameter of the balloon 113, 114 to a predetermined desired value. When the diameter of the balloon 113, 114 decreases unduly, the control device 49 acts to increase the height of the balloon portion 113, whereby the plying point X then functions to cause strand 8 a to be absorbed into the cord 0 at a slower rate, thereby increasing the diameter of the balloon 113, 114 to a pre determined desired value.

Although only a limited number of embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing specification, it is to be especially understood that various changes, such as in the relative dimensions of the parts, materials used, and the like, as well as the suggested manner of use of the apparatus of the invention, may be made therein without departing from the spirit and scope of the invention as will now be apparent to those skilled in the art.

What is claimed is:

1. Mechanism for twisting together two strands so as to form a two-ply strand, comprising a source of supply of a first strand and a support carrying a let-off strand package for a second strand, a rotatable shaft operable to rotate a loop of the first strand about to let-off package and also to ply the two strands together at a plying point, a first means for feeding the first strand at substantially constant speed into the loop, a second means for feeding the plied strand away from the plying point at substantially constant speed, and means engaging the second strand in advance of the plying point for subjecting the second strandin the run thereof immediately in advance of and extending to the plying point to substantially constant tension.

2. Mechanism as claimed in claim 1, comprising means responsive to changes in size of the loop to vary the tension of the first strand in the loop.

3. Mechanism as claimed in claim 2, wherein the loop is free for inward contraction throughout its length during normal operation of the mechanism.

4. Mechanism as claimed in claim 2, comprising an apex guide for the end of the loop remote from the shaft, an idle flyer having an arm with a guide through which the rotating strand passes, the idle flyer being located nearer to the apex guide than to the loop generating portion of the shaft, the guide on the idle flyer being so located that the first strand approaching such guide always lies at an angle of less than with respect to the plane of rotation of the guide, the angle being measured toward the projected axis of the shaft.

5. Mechanism as claimed in claim 2, comprising a flyer mounted on the shaft for rotation thereby, and

' wherein the strand passes from the loop to the flyer, and

the plying point is substantially fixed centrally of the shaft.

6. Mechanism for twisting together two strands so as to form a two-ply strand, comprising a source of supply of a first strand and a support carrying a let-off strand package for a second strand, a rotatable shaft operable to rotate a balloon of the first strand about the let-off package and also to ply the two strands together at a plying point, a first means for feeding the first strand at substantially constant speed into the balloon, a second means for feeding the plied strand away from the plying point at substantially constant speed, means engaging the second strand in advance of the plying point for subjecting the second strand in the run thereof immediately in advance of and extending to the plying point to sub- ;stantially constant tension, and means responsive to changes in the diameter of the balloon to vary the tension of the first strand in the balloon.

7. Mechanism for twisting together two strands so as to form a two-ply strand, comprising a source of supply of a first strand and a support carrying a let-off stran package for a second strand, a rotatable shaft operable to rotate a balloon of the first strand about the l tp j age and also to ply the two strands together at a plying point, a first means for feeding the first strand at substantially constant speed into the balloon, a second means for feeding the plied strand away from the plying point at substantially constant speed, means engaging the second strand in advance of the plying point for subjecting the second strand in the run thereof immediatel in advance 9 of and extending to the plying point to substantially constant tension, and means responsive to an increase in outward bulging of the balloon to decrease the tension of the strand in the balloon and responsive to a decrease in the outward bulging of the balloon to increase the tension of the strand in the balloon.

8. Mechanism for twisting together two strands so as to form a twoply strand, comprising a source of supply of a first strand and a support carrying a let-d strand package for a second strand, a rotatable shaft operabie to rotate a balloon of the first strand about the let-oi package and also to ply the two strands together at a plying point, a first means for feeding the first strand at substantially constant speed into the balloon, a second means for feeding the plied strand away from the plying point at substantially constant speed, means engaging the second strand in advance of the plying point for subjecting the second strand in the run thereof immediately in advance of and extending to the plying point to substantially constant tension, and means responsive to an increase in the outward bulging of the balloon to decrease the height of the balloon and responsive to a decrease in the outward bulging of the balloon to increase the height of the balloon.

9. A method of twisting together two strands so as to form a two-ply strand, comprising feeding a first strand from a first source of supply thereof, rotating a zone of the first strand in the form of a loop about a let-0d package for a second strand, withdrawing the first strand from the loop and bringing it into engagement with the second strand at a fixed plying point on the axis of the loop, feed- 10 ing the first strand at substantially constant speed into the loop, feeding the second strand to the plying point under substantially constant tension, and feeding the plied strand away from the plying point at substantially constant speed.

10. A method as claimed in claim 9, comprising detecting changes in the size of the loop, and varying the tension of the strand in the loop to restore the tension of the first strand in the run thereof immediately in advance of and extending to the plying point to substantially that or" the second strand in the run thereof immediately in advance of and extending to the plying point.

11. A method as claimed in claim 9, comprising decreasing the tension in the first strand in the loop upon an increase in the outward bulging of the loop and increasing the tension in the first strand in the loop upon a decrease in the outward bulging of the loop.

12. A method as claimed in claim 11, comprising increasing the tension in the first strand in the loop by increasing the height of the loop and decreasing the tension of the first strand in the loop by decreasing the height of the loop.

References Cited in the file of this patent UNITED STATES PATENTS 2,689,449 Clarkson Sept. 21, 1954 2,729,051 Clarkson Jan. 3, 1956 2,870,596 Vibber 1 Jan. 27, 1959 2,893,197 Vibber July 7, 1959 2,986,865 Clarkson June 6, 1961 3,108,427 Clarkson et a1. Oct. 29, 1963 

1. MECHANISM FOR TWISTING TOGETHER TWO STRANDS SO AS TO FORM A TWO-PLY STRAND, COMPRISING A SOURCE OF SUPPLY OF A FIRST STRAND AND A SUPPORT CARRYING A LET-OFF STRAND PACKAGE FOR A SECOND STRAND, A ROTATABLE SHAFT OPERABLE TO ROTATE A LOOP OF THE FIRST STRAND ABOUT TO LET-OFF PACKAGE AND ALSO TO PLY THE TWO STRANDS TOGETHER AT A PLYING POINT, A FIRST MEANS FOR FEEDING THE FIRST STRAND AT SUBSTANTIALLY CONSTANT SPEED INTO THE LOOP, A SECOND MEANS FOR FEEDING THE PLIED STRAND AWAY FROM THE PLYING POINT AT SUBSTANTIALLY CONSTANT SPEED, AND MEANS ENGAGING THE SECOND STRAND IN ADVANCE OF THE PLYING POINT FOR SUBJECTING THE 